Many electronic systems receive analog input signals through an input interface such as a transducer or probe. Examples of such systems include electronic test equipment, metrology equipment, recording devices, and many others. The analog input signals are generally converted into a digitized form for further analysis and processing. This conversion process is accomplished by an analog to digital converter (ADC).
The analog input signals are usually single-ended signals, but most high performance ADCs require differential signal inputs. Accordingly, before the analog input signals are provided to an ADC, they must be converted from single-ended form to differential form. The most common way to convert single-ended signals into differential signals is through the use of a balun transformer.
A balun transformer can convert high-frequency single-ended signals into differential signals without introducing significant distortion. However, a balun transformer cannot operate at low frequencies, so it cannot be used in systems requiring broadband signal conversion. As a result, many ADCs are designed to ignore signals at lower frequency ranges and to function only at higher frequency ranges. Such ADCs are commonly referred to as alternating current (AC) coupled or intermediate frequency (IF) ADCs.
Due to the limits of balun transformers, electronic systems requiring full spectrum single-ended to differential conversion typically rely on a commercially available or custom-built differential-in differential-out amplifier. Such amplifiers can be DC coupled to perform conversion in a frequency range between direct current (DC) and high frequency (HF).
Unfortunately, differential-in differential-out amplifiers tend to introduce noise and distortion across the full frequency range, even if they do not perform amplification, i.e., they have a gain of one. In addition, these amplifiers may present additional design difficulties because they often have output common mode voltage requirements that are different from input common mode voltage requirements of the ADC. Further, these amplifiers include active components, so may consume an undesirable amount of power.
In view of the above shortcomings of conventional techniques and technologies, new approaches are needed for converting single-ended signals into differential signals. In particular, new approaches are needed to provide broadband single-ended to differential conversion with reduced noise, distortion, and power consumption.